"After a 32-year battle with Parkinson's disease, Muhammad Ali has passed away at the age of 74," family spokesman Bob Gunnell said in a statement.

Ali was sent to hospital for a respiratory issue on June 2.

As one of the greatest boxers in the history, Ali retired in 1981 and was soon found signs of sluggishness and neurological damage. He received treatment for Parkinson's disease there after.

Ali, known as Cassius Clay before he converted to Islam, began boxing training at 12 years old and won the world heavyweight championship at 22 years old in 1964. He won the title again in 1974 and 1978.